Pollen Mineralization Fuels Biogeochemical Cycling and Microbial Community Succession in Lake Superior

Abstract

Pollen is a terrigenous particulate regarded as recalcitrant organic matter (OM) in aquatic ecosystems, seasonally introducing undetermined quantities of terrigenous OM to inland lakes. The role of pollen as a carbon and nutrient delivery mechanism for large aquatic ecosystems remains an understudied component of biogeochemical cycling. Here, we examined the effects of pollen mineralization on carbon and nutrient availability to evaluate its potential as an unquantified seasonal source and driver of microbial community succession in Laurentian Great Lake (LGL) Superior. Pollen was added to water collected from LGL Superior and incubated in the dark at 4°C for 60 days. Water samples were measured for dissolved and particulate fractions of carbon (C), nitrogen (N), and phosphorus (P) alongside ultraviolet-visible spectroscopy. Microbial community succession was assessed through metagenomic sequencing and abundance estimates at selected times. Results show immediate, significant increases in dissolved chemical fractions, with 21.0% of the initial weight of pollen C, 28.1% N, and 40.1% P chemically leaching. Extrapolated lake-wide, pollen leaching resembles a potential loading of up to 0.30 Tg C yr⁻¹, 17.3 Gg N yr⁻¹, and 1.64 Gg P yr⁻¹. Subsequent increases in estimated prokaryotic abundance and decreases in dissolved nutrients were accompanied by shifts in microbial community composition expressing increases of 5% amino acid and 10% carbohydrate metabolism over the experimental duration. These results suggest pollen contains labile OM fractions that are a substantial source of bioavailable carbon and nutrients that can fuel microbial succession and seasonal dynamics in large lakes.